1. Field of the Invention
The present invention relates generally to apparatus for controlling cursor movement on a video display terminal (VDT) and more particularly to a pointing stick apparatus which is integrated together with keyswitches on a computer keyboard so as to minimize the size of the keyboard.
2. Description of the Related Art
Prior art keyboard pointing devices for controlling a cursor on a VDT are known. For example, U.S. Pat. No. 4,680,577 to Straayer, et al. (the '577 patent) discloses a multi-purpose key on a computer keyboard for controlling the cursor. Strain gauges are coupled to the multi-purpose key, which also serves as a regular typing key, for sensing lateral forces applied by the user's fingertip for cursor control. One of the problems with prior art devices, even those that are force-sensitive, is that a user gets no response to lateral displacement initially, until an electrode makes initial contact, for example, with an elastomeric resistive layer. The initial contact causes a step response, as resistance drops from infinity to a measurable value--a jump the user may not have anticipated or desired. Then, as force is increased, resistance falls rapidly, over some range, and finally falls more slowly with the application of additional force. All of this is disconcerting to a user for most applications. U.S. Pat. No. 5,231,386 (the '386 patent) discloses a keyswitch-integrated pointing device in which the force sensors are "preloaded" to an operating state such that there is no "jump" when a user starts to point to move the cursor. International patent application PCT/US90/06831 owned by Lexmark International also shows pointing apparatus for use in a keyboard for cursor control.
Most prior art "joysticks" are not sensitive to vertical or "Z-axis" force, because they have a rigid pivot or support underlying the joystick handle. As a result, vertical force cannot be measured or detected. The '386 patent shows how to produce a signal proportional to vertical force. Such a signal can be used, for example, to control line width while drawing as a function of z-axis force on the pointing device.
One problem with the prior apparatus is that the multi-purpose keyswitch or integrated keyswitch combines typing and cursor control into the same keycap. Some users, however, prefer to have a separate, different control or button for cursor control. A separate button is advantageous because the computer can detect actuation of the cursor control as distinguished from typing. The prior art '577 patent, for example, required a separate switch to enable the pointing sensors, since they were built into the typing key. A separate "pointing stick" has this advantage and does not require another switch; it can remain always "on". However, a separate pointing stick takes up precious keyboard space. For example, some portable or laptop computers have a trackball below the spacebar or off the side of the keyboard. These are not convenient. The need remains therefore to provide a pointing stick for cursor control without taking any space on the keyboard.